S* c Royal Socig^X 



show the influence of root-excretions was Euphorbia Lathyris, which 

 would not grow in the same ground three years successively, sX^,, 

 though the soil was found afterwards fitted for rearing several othecu 

 species of plants. In the remaining cases, tliere was in general a.,; 

 marked difference between the permanent and the shifting crop, tq,> 

 the disadvantage of the former; and where exceptions occurred tPiji 

 this rule, they seemed capable of being accounted for by accidental,, 

 causes. The amount of each year's crop is given in a tabular form, 

 and their differences illustrated by diagrams showing the relation 

 between the two crops of each vegetable. ,.1,1,,,; 



The second part of the memoir commences with an account of thq, 

 method of analysis pursued by the author for determining the natureiq 

 and proportions of the ingredients present in the ashes of the cropsr, 

 submitted to examination. This method was, in general, similar to 

 that recommended by Will and Fresenius in their paper published 

 in the Memoirs of the Chemical Society * ; but in determining the 

 amount of phosphoric acid, the followif!g-W0t)fi,W3,s .a^^pt^d-in.pr.^;,. 

 ference to the one therein given. ,,;of) ..f/i tcfli Jnd : iiuijiiiUAiio:) nJi 



As the phosphoric acid would seize uponr^he iiipn in preferenq^,, 

 to any other base, the amount of peroxide of iron present in the asj^ , 

 was first determined by precipitating it from a muriatic solution by,,, 

 means of acetate of ammonia. The weight of the precipitate gives 

 that of phosphate of iron, from which that of the peroxide of iron,) 

 may be readily calculated. This being ascertained, he proceeds to.i 

 determine the phosphoric acid by operating on a fresh portion o^,; 

 the solution of the ash, into which a certain known weight of iroq,^ 

 dissolved in muriatic acid is introduced, in quantity more than suffi-:(, 

 cient to unite with the whole of the phosphoric acid present. This , 

 done, acetate of ammonia is added and the mixture boiled, when all 

 the peroxide of iron, whether combined with phosphoric acid or not, 

 is thrown down. From the weight of the precipitate, that of the 

 phosphoric acid present may be calculated, as both the amount of 

 peroxide of iron present in the ash, and that which was added sub- 

 sequently, are known. 



A report is then given of the analysis of the ashes of barley, of 

 the tubers of potatoes, of the bulbs of turnips, of hemp, of flax, and 

 of beans, all cultivated in the Botanic Garden ; and from the data 

 thus obtained, the quantity of inorganic matters abstracted from the 

 soil in ten years by the above crops is deduced : and a table is given 

 showing the relation between the permanent and shifting crops, with 

 respect to their produce, the amount of inorganic matters, that of 

 alkali, and that of phosphates, contained in them. 



In the third jxirt of his paper, the author considers the chemical 

 composition of the soil in which the above-mentioned crops were 

 grown. He states, in the first place, the method he adopted for de- 

 termining the amount of phosphoric acid present in the soil. 



An analysis is then given of the soil taken from a portion of the 

 garden contiguous to that in which the experiments were carried on, 

 and from one of the plots of the garden itself, and from these data 

 * See Phil. Mag. S. 3. vol. xxv. p. 500. 



